In recent years, attention is focused on a refrigeration cycle apparatus using, as refrigerant, carbon dioxide (CO2, hereinafter) in which ozone destroy coefficient is zero and global warming coefficient is extremely smaller than Freon.
There is proposed a refrigeration cycle apparatus using CO2 refrigerant in which expansion energy of a working medium is recovered using an expander instead of an expansion valve, thereby enhancing coefficient of performance of the refrigeration cycle apparatus. It is proposed to use a swash plate expander as this expander (see patent document 1 for example).
[Patent Document 1]
Japanese Patent Application Laid-open No.2001-141315 (FIG. 2)
In the present invention, a sliding vane type expander is employed as the expander. In the sliding vane type expander, since the vane jumps, a large sound is generated and a hitch is generated in a tip end of the vane. If a back pressure is insufficient, a leakage from the tip end of the vane is increased, and a leakage loss is generated.
Such problems are solved if lubricant discharged into a high pressure chamber is supplied to a back surface of the vane, but a structure for supplying the lubricant becomes complicated.
If a spring is disposed in a back surface of the vane, a reliability between contact surfaces of the spring and the vane is deteriorated, and if high pressure refrigerant gas is supplied, since the refrigerant is gas, the leakage loss is adversely increased.
It is an object of the present invention to provide an expander in which its structure is simple, the leakage loss is small and the expander is operated reliably, by utilizing refrigerant in the supercritical state.